1. Field of the Invention
The present invention relates to a spindle structure of a machine tool etc., and more specifically, to a technology to prevent noise which occurs when the spindle rotates at high speed.
2. Description of the Related Art
Generally, a spindle rotating at high speed has a tap hole for balance adjustment on an end surface or has other parts such as a dog for detecting a position mounted by a screw. Thus, when the spindle is rotated, there is a problem in which an external wind noise occurs due to the tap hole and a protruding head of the screw. To solve the problem, as disclosed in Japanese publication of unexamined patent application 2000-218465, a cover for covering the rotating portion, or a lid for covering the tap hole has been used.
However, the noise reduction effect is small even when the rotating portion is covered by a cover. Further, the lid protrudes from an edge of the spindle even when the tap hole is covered with the lid, resulting that external wind noises occur due to the protruded lid. Although the entire spindle is covered, the external wind noise reduction is small if the noise generated by the cover is considered. In other words, it is very difficult to reduce the noise completely.
In view of the above, the object of the present invention is to provide a spindle structure to effectively prevent a noise occurrence by a tap hole and a screw.